Installation and method for coating objects

ABSTRACT

An installation for coating objects, in particular vehicle wheels, has a dipping trough which is filled with a coating liquid into which the objects can be dipped. In order to reduce the complexity of the piping, there is provided a combined recirculation and filtration circuit for recirculating and filtering the coating liquid, wherein the recirculation and filtration circuit includes a pump, at least one recirculation outlet, arranged in the dipping trough, for the coating liquid, and a filtration device having a residue connection and a filtrate connection, wherein the residue connection is connected to the at least one recirculation outlet in the dipping trough.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/309,682 filed Nov. 8, 2016, which is a national phase ofInternational Pat. App. No. PCT/EP2015/000714, filed Apr. 1, 2015, whichclaims the filing benefit of German Pat. App. No. 10 2014 006 795.5,filed May 9, 2014—the contents of all of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to an installation for coating, in particular forelectrodeposition painting, of objects, in particular vehicle wheels,having

-   -   a) a dip tank which is filled with a coating fluid in which the        objects can be dipped.

The invention further relates to an associated method for coatingobjects.

2. Description of the Prior Art

Dip coating, in particular electrodeposition painting, is a methodwidely used in the automotive industry for coating objects, inparticular for painting vehicle bodyworks and components thereof, suchas, for example, the vehicle wheels.

During the electrodeposition painting operation, the objects areimmersed in a dip tank in a conductive, largely aqueous coating fluidand, by applying a voltage field between the immersed objects andelectrodes which are arranged in the dip tank, the coating process isstarted. The deposition of the paint on the objects is carried out inthis instance substantially via an electrochemical conversion of bindingagents and paint pigments as a result of the current flow between theelectrodes and the objects. Depending on the polarity, a distinction ismade between anode electrodeposition (AED) and cathode electrodeposition(CED).

During this electrochemical coating process, the composition of thecoating fluid changes locally on the objects, for example, as a resultof the discharge of the color pigments which bond to the coated objectsfrom the coating fluid. In order to nonetheless achieve a uniform andpredictable coating result, it is therefore necessary and known from theprior art to substantially continuously circulate the coating fluid inthe dip tank using a circulation system. The physical and chemicalparameters of the coating fluid in the entire dip tank are thereby keptin a homogeneous state.

By means of additional circuits, the parameters of the coating fluid arethen generally adjusted. Thus, it is, for example, known to provide afiltration circuit with which a small part-flow of the coating fluid iscontinuously purged of solid components, such as, for example, the paintpigments. This so-called retentate is added to the coating fluid againafter a corresponding preparation. In contrast, the filtrate, forexample, after adjusting the pH value, is used to clean the paintedobjects.

It is further known to provide a heat exchange circuit by means of whichthe heat which is introduced into the coating fluid by the electricalpower of the electro-deposition painting can be discharged again.

The disadvantage of the previously known solutions is that, for thedifferent circuits, there have to be provided complex pipework systems,which have to be freely accessible for maintenance purposes, whereby thecomplexity of the pipework is again increased.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide a simplifiedinstallation for coating in a dip tank.

This object may be achieved according to the invention by aninstallation set out in the introduction, in which:

-   -   b) a combined circulation and filtration circuit is provided for        circulating and filtering the coating fluid, wherein the        circulation and filtration circuit comprises        -   a pump having a pump inlet and a pump outlet, wherein the            pump inlet is at least indirectly connected to the dip tank,        -   at least one circulation outlet which is arranged in the dip            tank for the coating fluid, and        -   a filtration device whose inlet is connected to the pump            outlet of the pump and which has a retentate connection and            a filtrate connection, wherein the retentate connection is            connected to the at least one circulation outlet in the dip            tank.

The inventor has recognized that, in particular with installations forcoating smaller objects, such as, for example, vehicle wheels, it is notnecessary to provide separate flow circuits for the filtration and forthe circulation of the coating fluid. This is because, with asufficiently large sizing of the filter device, the deposited retentatecan also take over the function of circulating the coating fluid in thedip tank if it is supplied via circulation outlets into the dip tank. Inthis manner, the retentate which is supplied back produces the necessarybath movements of the coating fluid in the dip tank. Such circulationoutlets are known per se and preferably have injector nozzles by meansof which in particular in the bottom region of the dip tank there areproduced occurrences of turbulence which swirl around deposited solidcomponents of the coating fluid. Since according to the invention,therefore, only one combined circulation and filtration circuit isrequired instead of a plurality of separate circuits or part-circuits,the installation is on the whole simplified.

There is preferably provided an overflow tank into which the coatingfluid from the dip tank can overflow, wherein the pump inlet of the pumpis then connected to the overflow tank. In this manner, the coatingfluid is indirectly drawn from the dip tank, wherein as a result of anoverflow which is produced in this instance contaminations of thecoating fluid accumulate in the overflow tank.

The pump of the circulation and filtration circuit is preferablyconstructed as a submersible pump and arranged in the overflow tank.This has the advantage compared with the prior art that, with regard tothe sealing of the pump, a situation involving lesser requirements oreven no requirements at all has to be complied with. This is because,conventionally, with normal pumps of the circulation circuit, as aresult of the aggressive character of the coating fluid only labyrinthtype shaft seals can be used so that coating fluid which is dischargedat the seals of the pumps has to be discharged in an additional separatecircuit. A submersible pump acting as the pump of the circulation andfiltration circuit consequently again substantially simplifies thepipework of the installation.

In order to achieve a sufficiently high circulation flow in the coatingfluid, the retentate connection of the filter device and the circulationoutlet in the dip tank are preferably connected to each other without abuffer store being interposed. The combined circulation and filtrationcircuit can thus be operated with only one pump.

Furthermore, the filtration device may comprise an ultra-filtrationmodule, whereby a sufficiently cleaned filtrate is discharged.

The circulation and filtration circuit may comprise a temperaturecontrol device, in particular a heat exchanger, which is preferablyarranged upstream of the filtration device and by means of which heatcan be removed from or supplied to the coating fluid. In this manner, itis also possible to dispense with a separate heat exchange circuit forthe coating fluid, as conventionally used in the prior art.Alternatively, heat can be removed from or supplied to the coating fluiddirectly by means of a temperature control device which is arranged inthe dip tank, for example, a cooling coil.

Furthermore, there may be provided an additional counter-containercircuit which comprises a pump without any seals, in particular adiaphragm pump, by means of which the coating fluid, in particular formaintenance operations on the dip tank, can be conveyed to acounter-container and back again.

It is further advantageous for the filtrate connection of the filtrationdevice to be at least indirectly connected to a cleaning tank, in whichthe objects are cleaned after the coating operation. In this manner, thefiltrate, without additional pumps being necessary, can be used to cleanthe objects.

In this instance, there may be interposed between the filtrateconnection and the cleaning tank a buffer store in which filtrate whichaccumulates at the filtrate connection is retained for cleaningpurposes, in particular for manual cleaning purposes of theinstallation.

Finally, in particular with cathode electrodeposition painting, adialysis circuit which is independent of the combined circulation andfiltration circuit may be provided. This enables the acid content andthe conductivity of the coating fluid to be adjusted by means of theregulation of the throughput through the dialysis circuit.

It is to be understood that the aspects and objects of the presentinvention described above may be combinable and that other advantagesand aspects of the present invention will become apparent upon readingthe following description of the drawings and detailed description ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained below with reference to two embodiments andwith reference to the appended drawings, in which:

FIG. 1 is a schematic illustration of an installation for dip coatingvehicle wheels;

FIG. 2 is a schematic illustration of a modified installation having abuffer container for cleaning water.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail one or more embodiments with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the invention and is not intended to limit the invention to theembodiments illustrated.

FIG. 1 shows an installation which is generally designated 10 forcataphoretic dip coating of vehicle wheels 12.

The installation 10 comprises a dip tank 14 which is filled with anelectrodeposition paint 16 as a coating fluid. The vehicle wheels 12which are intended to be painted are lowered into the dip tank 14 usinga conveying device 18 which is only partially shown and therebypartially or completely immersed in the electrodeposition paint 16 whichis substantially composed of deionized water, binding agent and paintpigments and other known additives. By applying a voltage between thevehicle wheels 12 and electrodes 20 which are also arranged in the diptank 14, the coating process is started.

In addition to the dip tank 14, there is provided in this instance inthe form of a channel which extends along the dip tank 14 an overflowtank 22 into which excess electrodeposition paint 16, as indicated bythe flow arrow 24, can overflow. In this instance, conversion productsof the electrodeposition paint 16 which occur during the coating processand other impurities are carried along, whereby a crest of foam 26 isformed in the overflow tank 22 above the electrodeposition paint 16.

In order to prevent solid components of the electrodeposition paint 16,for example, the paint pigments, from being deposited in the dip tank 14and agglomerating in this case and in order to ensure that the physicaland chemical parameters of the electrodeposition paint 16 aredistributed in the dip tank 14 in a homogeneous manner, a circulationflow 32 is produced in the dip tank 14 using a combined circulation andfiltration circuit 30.

The circulation and filtration circuit 30 comprises to this end firstlya pump which is constructed in this instance as a submersible pump 34which is arranged in the overflow tank 22 and which has an inlet 35.From the outlet 37 thereof a line 36 leads to the primary side of a heatexchanger 38 whose secondary side is connected to a cooling system whichis not shown by means of lines 40, 42.

In the continuation of the flow path of the electrodeposition paint 16,a line 44 leads from the primary side of the heat exchanger 38 to afilter device 46, more specifically to a pre-filter 48 of the filterdevice 46. From this pre-filter 48, another line 50 leads to anultra-filtration module 52 of the filter device 46 which has a retentateconnection 54 and a filtrate connection 56 as outlets of the filterdevice 46.

The retentate connection 54 of the filter device 46 at which a retentatewhich is enriched with solid components is discharged is connected bymeans of a line 58 to one or more circulation outlets 60 which arearranged in the dip tank 14 and which are each provided with an injectornozzle 62. The circulation outlets 60 are in this instance arranged andsized in such a manner that, with corresponding sizing of the retentatethroughput (which is substantially controlled by means of the conveyingpower of the submersible pump 34), an adequate circulation flow 32 isproduced in the dip tank 14 in order to prevent settlement of solidcomponents and to achieve homogenization of the electrodeposition paint16.

However, the filtrate connection 56 of the filter device 46, at whichthe aqueous components of the electrodeposition paint 16 aresubstantially discharged as filtrate, is connected to a cleaning tank 66by means of a line 64. In this cleaning tank 66, the vehicle wheels 12are cleaned after the coating process in order, for example, to removenon-adhesive, excess paint. The cleaning water 68 which is thenpartially enriched again with paint pigments (contaminated filtrate) iscirculated in the cleaning tank 66 via an additional submersible pump 70which is arranged in the cleaning tank 66 and associated circulatingoutlets 60. Furthermore, from an overflow outlet 72 which is arranged inthe upper region of the cleaning tank 66, a line 74 leads to theoverflow tank 22 of the dip tank 14 in order to return excess cleaningwater 68 into the circulation and filtration circuit 30 of the dip tank14.

In order to introduce fresh electrodeposition paint 16 with preciselydefined chemical and physical parameters into the installation 10, itcomprises a supply line 75 into the dip tank 14 which is connected to apaint supply device which is not shown.

Since the acid content of the electrodeposition paint 16 increasesduring the coating process, a dialysis circuit 76 which cooperates withthe electrodes 20 (and which is only partially illustrated) is furtherprovided. This comprises tubular exchange diaphragms 78 which coaxiallysurround the mostly rod-like electrodes 20. The inner space of theexchange diaphragms 78 is then flushed with dialysis fluid during thecoating process in order to reduce the acid content.

Finally, the dip tank 14 is connected by means of a counter-containercircuit 80 to a counter-container 82 which can receive all theelectrodeposition paint 16 from the dip tank 14 and thus enables the diptank 14 to be completely emptied for maintenance purposes or the likewithout having to dispose of the electrodeposition paint 16. Thecounter-container circuit 80 comprises for this purpose a valvearrangement 84 and a diaphragm pump 86, wherein in a first position ofthe valve arrangement 84 the electrodeposition paint 16 can be conveyedby the diaphragm pump 86 from the dip tank 14 into the counter-container82. In a second position of the valve arrangement, the diaphragm pump 86together with circulation outlets 60 which are arranged in thecounter-container 82 can be used to produce a circulation flow 88 in thecounter-container 82 during the maintenance operations. In a thirdposition of the valve arrangement 84, the same diaphragm pump 86 can beused to return the electrodeposition paint 16 into the dip tank 14again.

FIG. 2 shows a slightly modified variant of the installation 10 in whichthe filtrate connection 56 of the filter device 46 is not directlyconnected to the cleaning tank 66. Instead, the line 64 extending fromthe filtrate connection 56 leads from that location to a buffercontainer 90 in which the filtrate is provided, for example, for manualcleaning purposes of the installation 10. Another line 92 on the bottomof the buffer container 92 then leads in a similar manner to theembodiment of FIG. 1 into the cleaning tank 66.

It is to be understood that additional embodiments of the presentinvention described herein may be contemplated by one of ordinary skillin the art and that the scope of the present invention is not limited tothe embodiments disclosed. While specific embodiments of the presentinvention have been illustrated and described, numerous modificationscome to mind without significantly departing from the spirit of theinvention, and the scope of protection is only limited by the scope ofthe accompanying claims.

What is claimed is:
 1. A method for coating objects, comprising thesteps of: a) immersing objects in a dip tank which is filled with acoating fluid, b) circulating and filtering the coating fluid in the diptank by removing at least a portion of the coating fluid from the diptank; filtering the coating fluid which has been removed from the diptank in a filtration device having a retentate connection and a filtrateconnection, whereby retentate and filtrate are separated in thefiltering device and the retentate accumulates at the retentateconnection and the filtrate accumulates at the filtrate connection;connecting the retentate connection to all of one or more circulationoutlets arranged in the dip tank; returning the retentate to the diptank through all of the one or more circulation outlets arranged in thedip tank; and generating a circulation flow within the coating fluid inthe dip tank by returning the retentate to the dip tank from theretentate connection through the one or more circulation outlets.
 2. Themethod of claim 1, wherein the coating fluid is maintained in ahomogenous state by the circulation flow formed by the returning ofretentate and circulating of the coating fluid by the one or morecirculation outlets.
 3. The method of claim 1, further comprising thestep of connecting the filtrate connection to a cleaning tank to providethe filtrate to the cleaning tank, the objects being cleaned in thecleaning tank after being immersed in the dip tank.
 4. The method ofclaim 1, further comprising the step of controlling the temperature ofthe portion of the coating fluid removed from the dip tank.
 5. Themethod of claim 1, further comprising the steps of: surrounding one ormore electrodes used to generate a voltage in the dip tank with one ormore exchange diaphragms, and providing dialysis fluid to the dip tankin order to reduce the acid content of the coating fluid in the diptank.
 6. The method of claim 1, wherein the portion of the coating fluidremoved from the dip tank is removed by overflowing from the dip tankinto an overflow tank, wherein the coating fluid which overflows intothe overflow tank is pumped from the overflow tank to the filtrationdevice.
 7. The method of claim 1, further comprising the step ofpre-filtering the portion of the coating fluid removed from the diptank, wherein the coating fluid is separated into the retentate and thefiltrated in an ultra-filtration module after being pre-filtered.
 8. Themethod of claim 1, wherein the one or more circulation outlets eachcomprise an injector nozzle.
 9. The method of claim 1, wherein theobjects are vehicle wheels.
 10. A method for coating objects, comprisingthe steps of: a) immersing objects in a dip tank which is filled with acoating fluid, b) circulating and filtering the coating fluid in the diptank by removing at least a portion of the coating fluid from the diptank; separating retentate and filtrate from the portion of the coatingfluid removed from the dip tank; accumulating the retentate at aretentate connection; connecting the retentate connection to all of oneor more circulation outlets arranged in the dip tank; returning theretentate to the dip tank through all of the one or more circulationoutlets arranged in the dip tank; and generating a circulation flowwithin the coating fluid in the dip tank by returning the retentate tothe dip tank from the retentate connection through the one or morecirculation outlets.
 11. The method of claim 10, wherein the coatingfluid is maintained in a homogenous state by the circulation flow formedby the returning of retentate and circulating of the coating fluid bythe one or more circulation outlets.
 12. The method of claim 10, furthercomprising the steps of: accumulating filtrate at a filtrate connection;and connecting the filtrate connection to a cleaning tank to provide thefiltrate to the cleaning tank, the objects being cleaned in the cleaningtank after being immersed in the dip tank.
 13. The method of claim 10,further comprising the step of controlling the temperature of theportion of the coating fluid removed from the dip tank.
 14. The methodof claim 10, further comprising the steps of: surrounding one or moreelectrodes used to generate a voltage in the dip tank with one or moreexchange diaphragms, and providing dialysis fluid to the dip tank inorder to reduce the acid content of the coating fluid in the dip tank.15. The method of claim 10, wherein the portion of the coating fluidremoved from the dip tank is removed by overflowing from the dip tankinto an overflow tank, wherein the coating fluid which overflows intothe overflow tank is pumped from the overflow tank to the filtrationdevice.
 16. The method of claim 10, wherein the one or more circulationoutlets each comprise an injector nozzle.
 17. An installation forcoating objects comprising: a) a dip tank which is filled with a coatingfluid in which objects can be dipped, wherein b) a filtration device forfiltering at least a portion of the coating fluid which is removed fromthe dip tank, wherein the filtration device comprises a pump having apump inlet and a pump outlet, wherein the pump inlet is at leastindirectly connected to the dip tank, a retentate connection whereretentate is accumulated, a filtrate connection where filtrate isaccumulated c) one or more circulation outlets arranged in the dip tankfor the coating fluid, wherein the retentate connection is connected toall of the one or more circulation outlets in the dip tank and theretentate is returned to the dip tank from the retentate connectionthrough all of the one or more circulation outlets.
 18. The installationaccording to claim 17, wherein the one or more circulation outlets eachcomprise an injector nozzle, wherein the one or more circulation outletsand injector nozzles generate a circulation flow in the dip tank, thecirculation flow maintaining the coating fluid in the dip tank in ahomogenous state.
 19. The installation according to claim 17, furthercomprising a heat exchanger, the heat exchanger controlling thetemperature of the portion of the coating fluid removed from the diptank.
 20. The installation according to claim 17, wherein the filtrateconnection of the filtration device is at least indirectly connected toa cleaning tank, in which the objects are cleaned after the coatingoperation, the filtrate being provided to the cleaning tank.